A light-modulating material is a material having a light transmittance varied by whether or not an electric field is applied to the material and having an incident light quantity adjustable thereby. Known is, for example, a light-modulating film wherein: a light-modulating layer is sandwiched between two transparent resin substrates; and the light-modulating layer is a layer having a light-modulating suspension in which light-modulating particles responsible to an electric field are dispersed, and a resin matrix in which the light-modulating suspension is dispersed (see Japanese Patent Application National Publication (Laid-Open) No. 8-503314).
This light-modulating film is a film wherein fine droplets of the light-modulating suspension, in which the light-modulating particles are dispersed, are dispersed in the resin matrix cured by the irradiation with ultraviolet rays. In this light-modulating film, the light-modulating particles absorb, scatter or reflect light by the Brownian movement thereof in the state that no electric field is applied thereto. Thus, the film cannot transmit incident light into the film. When an electric field is applied thereto, the light-modulating particles are polarized to be arranged in a parallel direction, correspondingly to the electric field. As a result, the film can transmit light radiated into the film.
In such a way, the transmission quantity of light is adjusted in the response of the light-modulating particles to an electric field.
As such a light-modulating film, know is a film wherein a light-modulating layer is formed directly between glass plates: such as a film obtained by forming a light-modulating layer on a polyester sheet, curing this, transferring the sheet-attached cured layer onto a glass plate covered with ITO, peeling the polyester sheet, and then sandwiching the cured layer between the glass plate and another glass plate equivalent thereto, which is described in JP-T-8-503314;
or a film formed by forming a light-modulating layer, about 50 μm in thickness, onto each of two glass substrates, each glass substrate having ITO applied thereonto, and then unifying these members in a vacuum (see Japanese Patent Application Laid-Open No. 9-113939). However, in such a method of forming a light-modulating layer directly onto a glass substrate, the working performance for forming the light-modulating layer onto a glass substrate is poor, especially, for example, when the glass substrate has a large area. Furthermore, the film thickness of the light-modulating layer is not easily made uniform; thus, it is difficult to yield a light-modulating film having a wholly uniform and excellent light-modulating performance.
As a light-modulating film for improving this, known is a light-modulating film obtained by applying a light-modulating material onto a polyester film having a surface on which an ITO transparent electrode film is formed, curing the light-modulating material to form a light-modulating layer, and then putting the resultant light-modulating layer attached film and a film which does not have any light-modulating layer onto each other, or putting light-modulating layer attached films yielded in the same way onto each other, so as to sandwich the light-modulating layer therebetween (see JP-A-2002-189123).
JP-A-2005-300962, JP-A-2006-64832 and so on include such an extensive description that the transparent substrates for sandwiching the light-modulating layer between them preferably have the thickness from 1 to 15 mm when the transparent substrates are each a glass piece, and the thickness from 10 to 1000 μm when the transparent substrates are each a polymeric film. However, sufficient investigations thereon are not made under the actual circumstances.